Glutaraldehyde indicator

ABSTRACT

An indicator capable of determining whether the concentration of a disinfectant/sterilant solution of glutaraldehyde exceeds a predetermined value comprising an indicator medium impregnated with a sulfite compound and an amino acid or an ammonium salt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 503,892, filedJune 13, 1983, now U.S. Pat. No. 4,521,376.

BACKGROUND OF THE INVENTION

While the most widely used method of sterilization in hospitals is steamsterilization, this method is not always practical, because of adverseeffects on materials to be sterilized. The long turn around timerequired for ethylene oxide sterilization often makes this alternativemethod not practical. A rapid, low temperature method for disinfectingand sterilizing surgical items relies on the use of an alkalineglutaraldehyde solution ("AGS") as the disinfectant/sterilant. Thesolution is generally used at a 2% concentration.

Studies indicate that the pH of the AGS solution affects both itsstability and its biocidal activity. At an acid pH of about 3-4,glutaraldehyde solutions are stable for a period of about two years.However, at low pH levels, AGS does not exhibit exceptional sporicidalactivity. The alkalinization of AGS on the other hand, while itoptimizes antimicrobial activity, as well as sporicidal activity,promotes an aldehyde polymerization reaction which results in a gradualloss of antimicrobial activity of the AGS.

AGS is considered biocidally active above one percent aldehydeconcentration. As a result of alkalination an AGS solution having aninitial glutaraldehyde concentration of 2.1% at a pH of 8.5 will degradeover a period of about 28 days at ambient temperatures to aconcentration of about 1.3% glutaraldehyde with a concommitant decreasein pH to about 7.4. This chemical degradation limits the useful life ofbuffered glutaraldehyde to 14 to 28 days depending on the nature andconcentration of the buffering agent.

Commercially, AGS is usually supplied at a glutaraldehyde concentrationof 2%. To insure effectiveness suppliers advise customers of theeffective life of the product, after which time it is recommended thatthe AGS be discarded. Illustrative of these commercial products andtheir recommended useful lives are the 2% GA shown in Table I.

                  TABLE I                                                         ______________________________________                                        Product                                                                       2% Glutaraldehyde      Recommended                                            (Trademark)      pH    Useful Life (Days)                                     ______________________________________                                        CIDEX            7.8   14                                                     CIDEX 7          7.9   28                                                     Glutarex         7.6   28                                                     *Wavicide        6.2   28                                                     ______________________________________                                         *unbuffered                                                              

Since excessive organic loads (blood, pus, mucus, etc.) reduce theeffectiveness of AGS, and reuse results in dilution of the solution as aresult of rinse water brought in with instruments and AGS removed uponremoval of the instruments, time alone is not necessarily determinativeof the degree of degradation of an AGS. The effect of these factors onAGS use life cannot be directly expressed quantitatively since thepertinent parameters are not readily measurable. Consequently, in orderto insure that the AGS is effective, hospital staff may discard AGS wellbefore the end of the recommended use life. It is known, however, thatto obtain kill in all samples of micro-organisms and viruses the lowestconcentration of glutaraldehyde which is effective is 1%.

All of the official methods for determining the effectiveness ofdisinfectants which have been established by the Association of OfficialAnalytical Chemists are complex, time consuming and beyond the technicalcapabilities of and time constraints on the nusing staffs which use AGS.A new effectiveness test for a particular brand of AGS, Cidex 7, wasintroduced into commercial distribution recently by Surgikos, Inc. Thetest method involves the use of a "kit" with a seven step procedurewhich includes the exact measurement of two reagents, the carefulmeasurement of two others, and a color comparison for determiningconcentration. A blue color is obtained when the glutaraldehydeconcentration falls to 1% or below, and is to be interpreted as the timeto replace the AGS. While this test is effective, the industry has longsought a simple "go-no go" test which can be carried out quickly withoutany need for special care or skill by the operator. Heretofore, no suchtest has been available.

SUMMARY OF INVENTION

An indicator for determining the effectiveness of a glutaraldehydesterilant comprising an absorbant medium which has been impregnated witha solution of sulfite compound and an amino acid or ammonium salt. Thepreferred sulfite is sodium sulfite. The preferred molar ratio ofsulfite to amino acid is about 2.5/1 to 20/1. Glycine is the preferredamino acid.

BRIEF DESCRIPTION OF DRAWING

FIGURE--The FIGURE depicts the preferred embodiment of the indicator ofthis invention.

DETAILED DESCRIPTION

This invention relates to an indicator for measuring the effectivenessof a glutaraldehyde sterilant. More specifically it relates to anindicator which is capable of differentiating between a 2% solution ofglutaraldehyde and solutions of lower concentrations. The glutaraldehydedisinfectants are generally alkalinated glutaraldehyde solutions. Whileunbuffered glutaraldehyde solutions are sterilants and within the scopeof this invention, they are not preferred since they tend to initiaterusting of instruments immersed in these solutions.

In its preferred embodiment the indicator of this invention comprises anabsorbant medium which has been impregnated with a solution of sulfitecompound and an amino acid. While a broad range of sulfite to amino acidratios can be used, the actual ratio will depend on the particularglutaraldehyde solution and the level at which differentiation betweensolutions of different concentrations is desired. A preferred ratio is10/1, more preferably 5/1.

The sulfite/amino acid ratio is not in itself determinative. Too littleamino acid available in the glutaraldehyde solution results in a lack ofdifferentiation between solutions of different concentrations. On theother hand, an excess of amino acid results in what is believed to beover-buffering of the indicator making it unresponsive to anyconcentration of glutaraldehyde in a practical time period; i.e., lessthan ten minutes.

The indicator can be mounted on any suitable backing strip e.g. plastic,metal foil, paper, etc. The indicator medium is preferably made of anabsorbant paper; e.g., chromotography paper. However, any water wettableabsorbant material may be used; e.g., polyester fabric, non-woven nylonfelt, Tyvek®, spun bonded poly propylene etc. Alternately, the indicatormedium may be an integral part of an absorbant medium at least one endof which has been impregnated with the impregnating solution. Apreferred material for the indicator medium is chromotography paper;e.g. S & S 410.

While of course an indicator medium in the form of a small pad may bedipped into the AGS to be tested using a tweezer or other means forholding the pad securely, in its preferred embodiment the pad is adheredto a backing strip.

Depending upon the ratio of sulfite to amino acid and the concentrationof amino acid the devices of this invention are responsive toglutaraldehyde concentrations as low as 0.75%. Hence, the indicator canbe adjusted to readily distinguish between solutions of glutaraldehydehaving concentrations in the 1-2% range. Such an indicator permitshospital nursing staff to confirm that an AGS being used is at aneffective concentration.

In its preferred embodiment the indicator of this invention is used todistinguish between 1% and 2% concentration of glutaraldehyde solutions.When dipped into a 2% solution of AGA a yellow color appears on theindicator pad, When the AGS solution has a concentration of 1% or lessof glutaraldehyde no color change is observed. Color change appears withsolutions between 1% and 2% glutaraldehyde. Hence, the indicator isspecific for a 1% concentration and permits hospital staff to know whenreplacement of AGS solutions must be made by a simple test technique.For this particular device the impregnating solution of choice comprisesa one molar solution of sodium sulfite and 0.2 molar amino acid. Thepreferred amino acids are glycine and lysine.

Tha advantages of the instant invention may be more readily appreciatedby reference to the following example.

EXAMPLE I

Solutions of sodium sulfite and amino acids were prepared and tested todetermine whether a color change capable of differentiation between a 1%and 2% AGS was discernable. In each case a water solution of 1.0M sodiumsulfite and 0.2M amino acid was prepared. Two cubic centimeters of thesolution was added to about 20 cc of 2% AGS (Cidex 7). The results aretabulated below.

                  TABLE II                                                        ______________________________________                                        Amino Acid        Observation                                                 ______________________________________                                        Alanine           N.C.*                                                       Arginine          N.C.                                                        D,L-Aspergine     N.C.                                                        Glutamine         N.C.                                                        Glycine           1 min. some yellow                                                            3 min. intense yellow                                       Leucine           N.C                                                         Lysine            1 min. some yellow                                                            3 min. some yellow                                          ______________________________________                                         *N.C. = no color change was observed after 24 hour of standing.          

EXAMPLE II

Example I was repeated using substituting para-aminobenzoic acid andtrihydroxy ammonium methane for the amino acid. No color change wasobserved in each case.

EXAMPLE III

Example I was repeated using glycine and lysine at 0.1M, 0.2 and 0.3Mthe results are tabulated below for both a 1% and 2% AGS(CIDEX-7).

                  TABLE III                                                       ______________________________________                                                 Amino Acid  AGS                                                      Amino Acid                                                                             Concentration                                                                             Concentration                                                                             Observation                                  ______________________________________                                        glycine  0.1         1%          some yellow                                           0.1         2%          some yellow                                           0.2         1%          N.C.                                                  0.2         2%          intense yellow                                        0.3         1%          N.C.                                                  0.3         2%          N.C.                                         lysine   0.1         1%          N.C.                                                  0.1         2%          N.C.                                                  0.2         1%          N.C.                                                  0.2         2%          some yellow                                           0.3         1%          yellow-orange                                         0.3         2%          yellow-orange                                ______________________________________                                    

At the 0.2M concentration both glycine and lysine were effective todifferentiate between a 1% and 2% solution of AGS.

EXAMPLE IV

A water solution of 1.0M sodium sulfite and 0.2M glycine was prepared.Strips of chromotography paper were saturated with the solution and airdried. The dried strips were dipped into test solutions of AGS,immediately removed and allowed to dry. Strips immersed in a 1% AGSshowed no color change. Strips immersed in a 2% AGS showed an intenseyellow color change in about two minutes.

EXAMPLE V

In order to determine the effectiveness of various concentrations andratios of sulfite to amino acid, a series of tests were performed in themanner of Example IV. In each case the sulfite and glycine levels werevaried. The test strips were evaluated by immersion into solutions ofCIDEX 7 and CIDEX of different concentrations of glutaraladehyde. Theresults are shown in Table IV. The following designations as used inTable IV have the specified meaning.

NR=no response in one hour

SY=strong yellow color

WY=weak yellow color

                                      TABLE IV                                    __________________________________________________________________________    Run No.   A     B    C    D    E    F                                         __________________________________________________________________________    Na.sub.2 SO.sub.3.sup.(1)                                                               2.0 M 2.0 M                                                                              2.0 M                                                                              0.5 M                                                                              0.5 M                                                                              1.0 M                                     glycine   0.4 M 0.2 M                                                                              0.1 M                                                                              0.2 M                                                                              0.1 M                                                                              0.2 M                                     Glutaraldehyde                                                                Concentration (%)                                                             2         NR/NR.sup.(2)                                                                       SY/SY                                                                              SY/WY                                                                              SY/SY                                                                              SY/SY                                                                              SY/SY                                     1.75      NR/NR SY/WY                                                                              SY/WY                                                                              SY/WY                                                                              SY/SY                                                                              SY/SY                                     1.5       NR/NR WY/WY                                                                              SY/WY                                                                              WY/WY                                                                              SY/SY                                                                              WY/WY                                     1.25      NR/NR NR/WY                                                                              SY/WY                                                                              WY/NR                                                                              SY/WY                                                                              WY/WY                                     1.0       NR/NR NR/NR                                                                              SY/WY                                                                              NR/NR                                                                              SY/WY                                                                              NR/WY                                     0.75      NR/NR NR/NR                                                                              WY/NR                                                                              NR/NR                                                                              WY/WY                                                                              NR/NR                                     __________________________________________________________________________     .sup.(1) Concentration of Na.sub.2 SO.sub.3 and glycine in the                impregnation solution used to prepare the indicator. The paper used is        chromotographcy paper.                                                        .sup.(2) The designations show the response for the indicator in CIDEX7       and CIDEX solutions. The designation before the slash mark (/) is the         response for CIDEX 7 while the designation after the slash is for CIDEX.      CIDEX is a trademark of Surgikos, Inc. for glutaraldehyde solutions used      as sterilants/disinfectants.                                             

As will be seen from the data where the concentration of amino acid inthe impregnating solutions is 0.4M the indicator is unresponsive tosolutions of glutaraldehyde of 2% or less concentration. At 0.1M aminoacid, however, the indicator is generally unresponsive, thoughdifferentiation is less precise than 0.2M solutions. At 0.2M amino acidconcentration the indicator readily distinguishes between varyingconcentrations of glutaraldehyde solution. This system is effective atsulfite to amino acid ratios of about 2.5/1 to about 20/1. Hence, theconcentration of amino acid in the impregnating solution which will givea response capable of differentiating between glutaraldehyde solutionsof different concentrations is about 0.1M to about 0.3M preferably 0.15Mto about 2.5M more preferably about 0.18M to about 2.2M, e.g. 0.2M.

EXAMPLE VI

In order to determine whether other organic amines are useful in thepractice of this invention, various amines were tested in the manner ofExample I at 1M Na₂ SO₃ and 0.2M amine. The response time at 1 hour wasnoted.

                  TABLE V                                                         ______________________________________                                        Amine             Responses (1 hr)                                            ______________________________________                                        Ortho-Aminophenol N.R.                                                        hexamethylene tetramine                                                                         N.R.                                                        melamine          N.R.                                                        dimethyl glyoxime N.R.                                                        2-amino-2-hydroxymethyl,                                                                        N.R                                                         1-3, propane diol                                                             trimethyl amine   N.R.                                                        2-2', dipryidylamine                                                                            N.R.                                                        diphenylamine     N.R.                                                        ______________________________________                                    

It is concluded that amines per se are not operative in the practice ofthis invention.

EXAMPLE VII

The experiments of Example IV were repeated substituting variousammonium compounds for the glycine. The results obtained with a 2%glutaraldehyde solution are shown in Table VI.

                  TABLE VI                                                        ______________________________________                                        Ammonium compound   Response                                                  ______________________________________                                        ammonium chloride   slight yellow- 3 min.                                     ammonium acetate    slight yellow- 3 min.                                     ammonium formate    slight yellow- 3 min.                                     ammonium bromide    slight yellow- 3 min.                                     ammonium bicarbonate                                                                              slight yellow- 3 min.                                     ______________________________________                                    

Hence, it is evident that ammonium compounds are effective substitutesfor the amino acids of this invention. As used in the specification andclaims, the term "ammonium compound" means ammonium salts of organic andinorganic compounds.

While the invention has been described in terms of sodium sulfite, anywater soluble sulfite salt is effective. The preferred sulfite compoundsare alkali metal sulfites and quarternary ammonium sulfites.Illustrative non limiting examples of such sulfites are sodium sulfite,potassium sulfite, lithium sulfite, tetra methyl ammonium sulfite andtrimethyl benzyl ammonium sulfite.

As used in the specification and claims the term "impregnate" means tosaturate with a solution and subsequently dry the medium which has beensaturated.

While in the case of the absorbant medium of this invention, thesulfites and amino acids as well as ammonium compounds are present onthe absorbant medium as dry compounds, these amounts can be quantifiedwith references to the solution from which they are deposited. Theabsorbant medium is saturated with the impregnation solution in thepreparation of the indicator and dried. Upon immersion for test purposesthe absorbant medium picks up substantially the same amount of liquidand generates a solution of substantially the same concentration as theimpregnating solution.

Where chromotography paper is the absorbant medium it takes up about 35micro liters of impregnating solution per square centimeter of paper.After drying and when used in tests the paper takes up about 35 microliters of glutaraldehyde solution, thereby generating a solution of thesame concentration of the indicator system; i.e., sulfite and amino acidor ammonium compound. In gram quantities the amount of amino aciddeposited on chromotography paper at solution concentrations of 0.1M to0.3M are about 1×10⁻⁴ to about 1×10⁻³ grams.

Where the quantity of dry compound on the absorbant medium is referredto in terms of molar concentrations, that reference is to the amountwhich would be deposited on the absorbant medium by saturating theabsorbant medium with a solution of the designated concentration.

It is known that the immersion time for disinfecting or sterilizing withand AGS is dependent on the pH of the AGS. Hence, in addition to knowingwhether the concentration of glutaraldehyde in the AGS is 1% or greater,the pH of the AGS must be known. This measurement can be made using anysuitable pH paper. For convenience the pH paper may be mounted on thebacking strip along with the indicator of this invention. This indicatorand pH paper may be mounted side by side on the backing strip, atopposite ends of the strip or on the same end with the pH indicator onone side and the indicator on the other. In this latter case a suitablebacking strip comprises a surlyn-mylar-surlyn sandwich.

Referring now to the FIG. I, a preferred embodiment of the indicator ofthis invention is shown. An indicator medium, 1, in the form of a padmade of a water wettable absorbant material is adhered to a backingstrip, 2, made of plastic or other material of suitable stiffness to actas a handle for the indicator pad. Optionally of pH paper, 3, is adheredto the reverse side of the backing strip.

The pad may be adhered to the backing strip by adhesive or heat sealing.For example, a backing strip comprising a laminate of mylar and surlynis heat sealed at one end with a strip of paper of suitable width byplacing the paper in contact with the surlyn surface and heat isapplied. The paper is then saturated with the impregnating solution andair dried. Mylar® is a terphthalic acid-ethylene glycol polyester andsurlyn® is a carboxylic acid inomer.

In a preferred embodiment the absorbant medium is heat bonded to aplastic layer of surlyn/mylar, impregnated with indicator solution andair dried. Subsequently, this indicating material is adhesively bondedto a backing strip which is preferably a non-absorbant rigid body, e.g.polyester film.

It will be evident from this disclosure that the solutions themselveswill act as glutaraldehyde indicators. For example, an indicatorsolution of 0.1M Na₂ SO₃ and 0.2M glycine can be furnished in a measuredamount in a vial. In order to test a glutaraldehyde solution foreffectiveness, the operator need only add a measured amount ofglutaraldehyde to the indicator solutions and observe the responseobtained. Alternately, the dry chemicals, e.g. Na₂ SO₃ and glycine, maybe preweighed at the Na₂ SO₃ /glycine ratios of this invention, andplaced in a vial. In order to test an AGS for effectiveness, theoperator need only add a predetermined measured amount of AGS solutionand observe the response. The amount of AGS solution utilized insufficient so that the concentration of available glycine in the AGS isabout 0.1M to about 0.3M, more preferably about 0.15M to about 0.25Me.g. 0.2M.

Of course neither the sulfite compound nor the amine compound of thisinvention used alone give a color response. Hence, the sulfite/aminecompound composition of this invention is a synergistic combination.

What is claimed is:
 1. A glutaraldehyde indicator solution comprising asolution of a sulfite compound and an amine compound wherein the aminecompound is (1) an amino acid where the amino acid is lysine or glysineor (2) an ammonium compound; said sulfite and amine compounds beingpresent in an amount effective to distinguish between glutaraldehydesolutions of different glutaraldehyde concentrations.
 2. The indicatorsolution according to claim 1 wherein the sulfite and amine compoundsare present at a molar ratio of sulfite to amine compound of about 2.5/1to about 20/1.
 3. The indicator solution according to claim 2 whereinthe molar ratio of sulfite to amine compound is 5/1.
 4. The indicatorsolution according to claim 1 wherein the concentration of aminecompound in the solution is about 0.1M to about 0.3M.
 5. The indicatorsolution according to claim 4 wherein the amine compound concentrationis about 0.15M to about 0.25M.
 6. The indicator solution according toclaim 5 wherein the amine concentration is 0.2M.
 7. The indicatorsolution according to claim 1 wherein the amine compound is glycine orlysine.
 8. The indicator solution according to claim 1 wherein the aminecompound is an ammonium compound.
 9. The indicator solution according toclaim 1 wherein the ammonium compound is ammonium chloride, ammoniumbromide, ammonium bicarbonate, ammonium acetate or ammonium formate. 10.The indicator according to claim 2 wherein the sulfite to amine compoundratio is 5/1, the amine compound ia glycine, the sulfite is sodiumsulfite and the concentration of glycine in the solutions is 0.2M.
 11. Aglutaraldehyde indicating composition comprising an intimate mixture ofa sulfite compound and an amine compound wherein the amine compound is(1) an amino acid, where the amino acid is glycine or lysine, or (2) anammonium compound; and wherein said sulfite and amine compounds arepresent in an amount effective to distinguish between glutaraldehydesolutions of different glutaraldehyde concentrations.
 12. Thecomposition according to claim 11 wherein the amine compound is an aminoacid.
 13. The compound according to claim 11 wherein the molar ratio ofsulfite compound to amine compound is about 2.5/1 to about 20/1.
 14. Thecomposition according to claim 12 wherein the amino acid is glycine. 15.The composition according to claim 13 wherein the ratio is about 5/1.16. The composition according to claim 11 wherein the sulfite compoundis Na₂ SO₃.